TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean Earthquake and Tsunami and Lessons learned therefrom (Proposals) October 2012 Japan Nuclear Safety Institute

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

Table of contents 1. Introduction ___ 2
2. Overview of Fukushima Daini Nuclear Power Station ___ 4
2.1 Overall Layout ___ 4
2.2 System Configuration ___ 5
2.3 Power Supply System ___ 7
2.4 Severe Accident Countermeasures; Accident Management ___ 9
3. Overview of the tsunami caused by the Tohoku-Pacific Ocean Earthquake ___ 11
3.1 Overview of the Earthquake and the tsunami ___ 11
3.2 Results of observation at Fukushima Daini ___ 15
3.3 Data on the earthquake and subsequent tsunami ___ 16
3.4 Damage of Equipment ___ 17
3.4.1 Damage by the earthquake ___ 17
3.4.2 Damage by the tsunami ___ 19
4.

Response to the accident at Fukushima Daini ___ 23
4.1 Response status from the time of the earthquake and tsunami until restoration and cold shutdown ___ 29
4.2 Emergency response situation ___ 30
4.2.1 Immediately after the earthquake ___ 30
4.2.2 Immediately after the arrival of the tsunami ___ 33
4.2.3 Responses toward restoration after the arrival of the tsunami ___ 34
4.2.3.1 Overview of the power plant ___ 34
4.2.3.2 Situation of Fukushima Daini Unit 1 ___ 38
4.2.3.3 Situation of Fukushima Daini Unit 2 ___ 39
4.2.3.4 Situation of Fukushima Daini Unit 3 ___ 41
4.2.3.5 Situation of Fukushima Daini Unit 4 ___ 42
4.3 Cooling of spent fuel pool of Fukushima Daini ___ 44
5.

Analysis of accident response ___ 45
5.1 Purpose of the analysis of accident response ___ 45
5.2 Concept of analysis ___ 45
5.3 Specific analysis procedures ___ 46
5.4 Important lessons obtained from the analysis ___ 59
6. Emergency response as seen from the viewpoint of the human factor ___ 61
7. Lessons ___ 64
7.1 Organization, management, communication ___ 64
7.2 Advance preparation (equipment, manual, training ___ 65
7.3 Initial response in the accident ___ 66
7.4 Additional measures ___ 67
8. Conclusion ___ 68
Attachment Recommended Actions for the Emergency Response by Equipments/Materials Reinforcement .

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

1. Introduction. For everyone associated with nuclear power, March 11, 2011 has become a day which will never be forgotten. This day will be long remembered by those in the nuclear industry for years to come. Even now, a large number of people still have to endure stressful lives as refugees. If we consider the length of time as well as the size and range of the damage, we will profoundly recognize the enormity of the damage of the nuclear disaster. Meanwhile, TEPCO’s Fukushima Daiichi Nuclear Power Station (hereinafter referred to as "Fukushima Daiichi"), is in the middle of a restoration process for accident convergence in accordance with the roadmap, and the situation of the power plant may be considered to have subsided substantially.

National agencies, local governments, industries, academia, volunteer groups and local residents are making efforts for decontamination and other tasks toward the restoration of the region, and as a result, some areas have managed to relax access restriction. Although there were the most stringent controls on the shipment of food from the outset of the accident, restrictions have been lessened little by little but it is still necessary to continue the constant monitoring. The level of radiation to which residents are exposed is regulated based on knowledge of the dose rate obtained from historical data, including survivors of the atomic bombs dropped on Hiroshima and Nagasaki, but this is not considered to provide clarity in indicating the late-onset effects of radiation exposure, and we do not think that a situation will develop in which there will be significant increase in cancer incidence due to radioactive materials.

The national government will continuously monitor the health of residents in the future. Extensive validations have been performed about the Fukushima Daiichi accident, and many reports have been published. Our Institute has also issued a proposal with the cooperation of TEPCO and manufacturers which was published at the end of last October as a statement from the industry. It focuses primarily on the hardware to combat tsunami to prevent accidents from expanding. We believe that the expansion of this accident and the massive release of radioactive materials into the environment could have been prevented if appropriate measures had been taken.

Dr. Hatamura, Chairman of the Accident Investigation Committee of the government, stated in a special NHK program that "this accident at Fukushima Daiichi could have been averted if proper and adequate preparations had been in place.” There is an ongoing national discussion of what to do about the energy supply in the future; we think that inexpensive natural energy is not sufficient at present, and will not be secure in the future, and that considering big problems such as energy security, global warming, and remaining internationally competitive (the hollowing out of domestic industry), it would be unrealistic to eliminate all nuclear power entirely.

Before the accident at Fukushima Daiichi, the Democratic Party, the current ruling party, promised the international community a 25% reduction of CO2 emissions and was planning to increase the proportion of nuclear power to 40%. How we can achieve our international commitment to CO2 reduction without nuclear power? And how long we can continue to pay as much as three trillion yen each year to operate thermal power plants instead of nuclear power plants, in addition to buying fossil fuels? In view of these difficult issues, we think that the realistic option for the time being is to continue using nuclear power while improving its safety.

Following the industry report analyzing the Fukushima Daiichi accident, our Institute decided 2

to validate the post-tsunami response situation at the Fukushima Daini Nuclear Power Station (hereinafter referred to as "Fukushima Daini") which successfully led the station to convergence, both from a technical perspective and from the viewpoint of a third party, with the intent of gathering lessons in order to enhance the accident response capability of nuclear power plants and contribute to the improvement of safety. Details of the sequence of events and responses to the Fukushima Daini accident have already been fully described in the accident analysis reports such as by the Government and by TEPCO.

Therefore, this report is dedicated to summarizing the overview of the sequence of events and accident responses, and it is intended to pick out good practices which include lessons for the future. In compiling these lessons, we tried to make our recommendations as specific as possible by describing the necessary level of preparedness based on the actual accident responses.

We hope that the lessons of this report will be utilized when nuclear power plants in Japan and throughout the world consider possible measures against accidents. As stated above, our report on the Fukushima Daiichi accident, which primarily summarizes the hardware and recommends various measures, is available at the Japan Nuclear Safety Institute’s website (former Japan Nuclear Technology Institute). Please visit the page. In this report, we basically excluded the analysis of the activities of the central and local governments and confined our analysis to gathering lessons about aspects to which electric utility companies should be able to respond.

2. Overview of Fukushima Daini Nuclear Power Station 2.1 Overall Layout Fukushima Daini is located in the towns of Naraha and Tomioka in Futaba-gun, Fukushima Prefecture, about 12 km south of Fukushima Daiichi, facing the Pacific Ocean to the east. The site is approximately 147 million m2 and its shape is almost square. At present, four units of boiling water reactors have been installed and are arranged in the order of No. 1, 2, 3, and 4 from the south. The generating capacity of these units is 1,100 MW each, making for a total installed capacity of power generation of 4,400 MW.

When the recent disaster occurred, all units 1 to 4 were in operation at the rated thermal output.

One central control room controls two units of reactors in a twin plant design: Units 1 and 2 make up one pair and Units 3 and 4 another. Type Location Unit Start of Operation Reactor Pressure Vessel Output(MW) Situation when event happened 1 S57.4 Mark II 1,100 Naraha town 2 S59.2 1,100 3 S60.6 1,100 Tomioka town 4 S62.8 BWR5 Mark II R Advanced 1,100 In operation at the rated thermal output Fig 2.1 Overall Layout of Power Stations Waste Treatment Building Unit 4 Unit 3 Unit 2 Unit 1 Main Office Building Important Seismic Isolation Building Reactor Building Turbine Building Seawater Heat Exchanger Building 4

2.2 System Configuration The system configuration of each unit of Fukushima Daini is as shown in Fig 2.2. The role of each system is as follows:
  • Reactor Core Isolation Cooling System (RCIC) In the event that the main condenser is no longer available for any reason, such as closure of the main steam isolation valve during normal operation, steam from the reactor will activate the turbine drive pump to inject the water in the condensate storage tank (referred to as "CST" below) into the reactor, and reduce the pressure by removing the decay heat of the fuel. The system also works as an emergency water injection pump in case of the failure of the water supply system, etc., and maintains the water level in the reactor.
  • Residual Heat Removal System (RHR) After shutting down the reactor, the system will cool the coolant (remove the decay heat of the fuel) using pumps and the heat exchangers, or maintain the level of reactor water by injecting cooling water in case of an emergency (part of ECCS). The system has the ability to bring the reactor to cold shutdown and has five modes of operation: reactor shutdown cooling mode, low-pressure injection mode (ECCS), containment spray mode, pressure suppression chamber cooling mode, and emergency heat load mode.
  • Emergency Core Cooling System (ECCS) The system consists of four subsystems: low pressure core spray system (LPCS), low pressure water injection system, high pressure core spray system (HPCS) and automatic depressurization system. In the case that a loss-of-coolant accident (LOCA) has occurred due to a piping break in the reactor coolant pressure boundary, such as the primary loop recirculation system piping, the system will remove the residual heat and the decay heat of the fuel in the reactor core, preventing the fuel cladding tube from being damaged by the fuel overheating, and consequently, minimize and suppress the water-zirconium reaction to a negligible extent.

Standby Liquid Control System (SLC) If and when control rod insertion becomes impossible for any reason during reactor operation, the system will inject a neutron-absorbing boric acid solution from the bottom of the reactor core as a backup for the control rod to stop the nuclear reaction. 5

Fig 2.2-1 System configuration of Fukushima Daini Unit 1 and 2 Fig 2.2-2 System configuration of Fukushima Daini Unit 3 and 4 RCIC Pump Water Pump (Turbine driven, 2 units) CST, from Suppression Pool Water Pump (Motor driven, 2 units) to Suppression Pool Condensate Pump (High Pressure, 3 units) (Low Pressure, 3 units) Main Turbine Condenser Circulating Water Pump (3 units) Sea Condensate Storage Tank (CST) to RHR MUWC Pump *2 to HPCS RCIC CRD *1 PLR (A) in Unit1, PLR (B) in Unit 2 *2 Pump three units in Unit 1, two units in Unit 2 from MUWC Pump to RHR (B) Pump HPCS Pump RHR (A) Pump to RCIC CRD Pump, 2 units from CST from CST SLC Tank SLC Pump, 2 units LPCS Pump from PLR (A) RHR (B) Pump RHR (C) Pump to Suppression Pool RCIC Pump Water Pump (Turbine driven, 2 units) Water Pump (Motor driven, 2 units) Condensate Pump (3 units) Main Turbine Condenser Circulating Water Pump (3 units) Sea Condensate Storage Tank (CST) to RHR MUWC Pump (3 units) to HPCS RCIC CRD from MUWC Pump to RHR (B) Pump HPCS Pump RHR (A) Pump to RCIC CRD Pump, 2 units from CST from CST SLC Tank SLC Pump, 2 units LPCS Pump from PLR (B) RHR (B) Pump RHR (C) Pump CST, from CST, S/P 6

2.3 Power Supply System The electricity generated by these units is transmitted via two 500 kV lines (Tomioka Line) to the power grid. The transmission capacity of one Tomioka line is sufficient for all the electricity generated at Fukushima Daini, and therefore the power plant can continue full output generation even in the case of failure in one transmission line. The power plant receives the power for starting and shutting down the reactor via two Tomioka Lines as the main circuits, or via two 66 kV lines (Iwaido Line) as the backup circuit.

In the event of a blackout of these two Tomioka Lines and two Iwaido Lines, the emergency electricity to safely shut down the reactor is powered by emergency diesel generators (D/G) and D/G in the high pressure core spray system (HPCS).

The Iwaido and Tomioka lines are shared by all units. 7

Fig 2.3-1 Power system diagram, skeleton diagram of emergency power system 500 kV Tomioka Line 66 kV Iwaido Line Series 1 Series 2 Series 1 Series Unit 1 Unit 2 Unit 3 Unit 4 High Voltage Startup Transformer Startup Switching Station 66 kV Electric Boiler Switching Station Startup Transformer 1SA Startup Transformer 1SB Startup Transformer 3SA Startup Transformer 3SB 6.9 kV M/C 1SA-1 6.9 kV M/C 1SA-2 6.9 kV M/C 1SB-1 6.9 kV M/C 1SB-2 6.9 kV M/C 3SA-1 6.9 kV M/C 3SA-2 6.9 kV M/C 3SB-1 6.9 kV M/C 3SB-2 Circuit Breaker ON Circuit Breaker OFF (Standby) Charging HPCS Pump *1 D/G(HPCS) D/G D/G(A) D/G(B) Unit 1 Note Note:※1,※3,※5 shall be replaced to read; Replace to read Unit 1 Unit 2 Unit 3 Unit 4 *1 *2 *7 *8 *3 *4 *9 *10 *5 *6 *11 *12 *3 D/G *5 D/G HPCS Pump HPCS Pump LPCS Pump RHR Pump (A) EECW Pump (A) RHR Pump (B) RHRC Pump (A) RHRC Pump (C) RHRS Pump (A) RHRS Pump (C) RHR Pump (C) EECW Pump (B) RHRC Pump (B) RHRC Pump (D) RHRS Pump (B) RHRS Pump (D) 8

2.4 Severe Accident Countermeasures; Accident Management Table 2.4 describes Fukushima Daini’s accident management. Countermeasures are prepared to mitigate the effects in the event that the situation has expanded to a severe accident. Table 2.4 Established Severe Accident Countermeasures Function Severe Accident Countermeasures Recirculation Pump Trip (RPT) Reactor shut down Alternate Rod Injection (ARI) Alternate Water Injection (Water injection into reactor core/containment vessel by make-up water pump/fire extinguishing pump ) Water injection to reactor core and containment vessel Automatic Depressurization of reactor core.

(Additional interlock in ADS) Alternate heat removal (Utilization of D/W cooler/reactor coolant cleanup system) Restoration of damaged equipment in the residual heat removal system (Procedure) Heat removal from containment vessel Hardened Vent Power sharing (accommodation of 480 V power from the adjacent plant) Support for safety functions Restoration of damaged equipment in the emergency D/G (Procedure) 9

Fig 2.4-1 Alternate Water Injection Fig 2.4-2 Hardened Vent Suppression Pool D/W Stack Reactor Building Exhaust Duct Standby Gas Treatment System (SGTS) Rupture Disk Inert Gas System (Containment Vessel Boundary) SGTS System : Boundary of System Abbreviations RPV : Reactor Pressure Vessel RCIC : Reactor Core Isolation Cooling LPCI : Low Pressure Coolant Injection RHR : Residual Heat Removal Diesel Driven Pump Filtered Water Tank Electric Pump Electric Pump Condensate Storage Tank FP System MUWC System Boundary of System RHR System MUWC System RHR MUWC System FP System RCIR LPCI Water Injection Pedestal Water Injection Suppression Pool D/W RPV 10

3. Overview of the tsunami caused by the Tohoku-Pacific Ocean Earthquake 3.1 Overview of the Earthquake and the tsunami The Tohoku-Pacific Ocean Earthquake, which occurred on March 11, 2011, was the biggest earthquake that has ever been observed in Japan in terms of the main shock. In this earthquake, a maximum seismic intensity of 7 was observed in Kurihara City, Miyagi Prefecture. High tsunamis were observed on the coast of Pacific Ocean in Hokkaido, Tohoku, and the Kanto region. The focal region of this earthquake ranges from offshore Iwate Prefecture to offshore Ibaraki prefecture, with a size of about 500 km in length and about 200 km in width.

The length of maximum slippage was estimated at more than 50 m.

In this earthquake, several large slippages were observed in the offshore of the southern part of Sanriku near the trench, the northern part of Sanriku, and some areas off the coast of the Boso Peninsula near the trench, evidencing that multiple focal regions off the coast of central Sanriku, Miyagi, Fukushima, and Ibaraki concurrently slipped to generate a mega-earthquake of magnitude 9.0 (the fourth largest ever observed in the world). The Headquarters for Earthquake Research Promotion, a national center for the research and study of earthquakes and tsunamis, had been monitoring and evaluating the ground motion of individual regions with case records in the past, but had not assumed for the condition of quakes occurring in all of these areas in conjunction.

The Expert Committee of the Central Disaster Management Council has also asserted that this enormous earthquake with a magnitude of 9.0 occurred with several source regions linking together in conjunction, which could not have been assumed from the past few hundred years of our country’s earthquake history.

The tsunami that occurred due to this earthquake and caused the most extreme devastation along the Pacific Ocean coast in the northeastern region of Japan was a magnitude 9.1 on the tsunami scale, making it the fourth largest ever observed in the world and the largest in Japan. 11

Earthquake off Sanriku, March 11, 2011 2:46 pm Seismic Intensity Map Source: Japan Meteorological Agency (Earthquake off Sanriku, March 11, 2011 2:46 pm Seismic Intensity Map) Legend Seismic Intensity 7 Seismic Intensity 6+ Seismic Intensity 6- Seismic Intensity 5+ Seismic Intensity 5- Seismic Intensity 4 Seismic Intensity 3 Seismic Intensity 2 Seismic Intensity 1 Epicenter 12

Source: Japan Meteorological Agency (March 2011 Earthquake and Volcanic Activity Monthly Report) The tsunami is thought to have occurred due to the seabed almost directly above the epicenter rising by about 3 m. The maximum height of tsunami run up above sea level was observed at nearly 35 m in northern Miyako city. The height of the flooding in the northern part of Miyako city was more than 25 m, and there were 58 km2 of flooded areas in Iwate, 327 km2 in Miyagi, 112 km2 in Fukushima, and 23 km2 in Ibaraki.

Seismic Source Time Function sec. Starting point of bedrock destruction in the main shock Epicenter of M7+ shock after March 9 Epicenter of M5+ shock within 1 day after main shock Center of each small fault Observation Point used in the analysis Slippage (m) Contour Interval: 4 m 13

  • Source: Excerpt from the 1st Meeting Material by The Investigation Committee on the Countermeasures learned as Lessons from the Tohoku-Pacific Ocean Earthquake As of July 31, 2012, the damage caused by the earthquake and the tsunami is enormous: 15,867 dead, 2,903 missing, 130,445 buildings totally destroyed, and 264,110 buildings partially destroyed. Aomori Prefecture Evidence of Tsunami [ Legend ] Offshore Tohoku Flood Height Offshore Tohoku Run-up Height (Source)
  • 2011 Tohoku-Pacific Ocean Earthquake Flood Height and Run-up Height : Preliminary Figures by "Joint Investigation Group on Tohoku-Pacific Ocean Earthquake and Tsunami" (May 9, 2011) Remarks: Based on the Data with Reliability Level A (Highly reliable with clear trace and minimal measurement error) obtained within an area of 200 m from the shoreline.

Iwate Prefecture Miyagi Prefecture Fukushima Prefecture Ibaraki Prefecture Hachinohe Miyako Rikuzentakata Sendai Flood Height and Run-up Height Run-up Height Flood Height Embankment Sea level at the time of tsunami arrival Tokyo Peil: Mean sea level at Tokyo Bay (T.P.) Flood Height: Height from the sea level at the time of arrival of the tsunami to the traces of tsunami inundation Run-up Height: Height from the sea level at the time of arrival of the tsunami to the traces of tsunami run-up. 14

3.2 Results of observation at Fukushima Daini The observed values of ground motion at the foundation of the reactor building (the lowest basement floor) of Fukushima Daini was below the maximum acceleration of design earthquake ground motion Ss (the maximum acceleration observed was 305 Gal on the B2 floor of the Unit 1 reactor building), and therefore this ground motion can be considered to be within the expected range of the seismic safety evaluation of the equipment.

Furthermore, using the recorded values of ground motion at the free field obtained during the earthquake, a soil structure model was identified for the strip analysis. As a result, ground motion of the strip analysis proved to be generally at the same level as actual observations, although the calculated values exceeded the design earthquake ground motion Ss in some of the periodic bands.

Exemplification of larger horizontal direction in table Fig. 3.2-1-1 Time History of Acceleration on the Ground Level of Reactor Building, Unit 1 (NS Direction) Fig. 3.2-1-2 Time History of Acceleration on the Ground Level of Reactor Building, Unit 2 (NS Direction) Fig. 3.2-1-3 Time History of Acceleration on the Ground Level of Reactor Building, Unit 3 (NS Direction) Fig. 3.2-1-4 Time History of Acceleration on the Ground Level of Reactor Building, Unit 4 (NS Direction) Fig. 3.2-2-1 Response Spectrum on the Ground Level of Reactor Building, Unit 1 (NS Direction) Fig. 3.2-2-2 Response Spectrum on the Ground Level of Reactor Building, Unit 2 (NS Direction) Fig.

3.2-2-3 Response Spectrum on the Ground Level of Reactor Building, Unit 3 (NS Direction) Fig. 3.2-2-4 Response Spectrum on the Ground Level of Reactor Building, Unit 4 (NS Direction) Time (sec.) Time (sec.) Time (sec.) Time (sec.) Acceleration (Gal) Acceleration (Gal) Acceleration (Gal) Acceleration (Gal) Cycle (sec.) Cycle (sec.) Cycle (sec.) Cycle (sec.) Acceleration (Gal) Acceleration (Gal) Acceleration (Gal) Acceleration (Gal) Recorded Measurement Basic Seismic Movement Ss-1 Basic Seismic Movement Ss-2 Basic Seismic Movement Ss-3 Recorded Measurement Basic Seismic Movement Ss-1 Basic Seismic Movement Ss-2 Basic Seismic Movement Ss-3 Recorded Measurement Basic Seismic Movement Ss-1 Basic Seismic Movement Ss-2 Basic Seismic Movement Ss-3 Recorded Measurement Basic Seismic Movement Ss-1 Basic Seismic Movement Ss-2 Basic Seismic Movement Ss-3 15

  • 3.3 Data on the earthquake and subsequent tsunami (1) Date and time of occurrence March 11, 2011, 2:46 pm (2) Epicenter Off the coast of Sanriku (38.1 N/142.9 E, 130 km ESE of Oshika Peninsula, focal depth 24 km) (3) Magnitude 9.0 (4) Peak ground acceleration 305 Gal at B2 floor of the Unit 1 reactor building (Vertical) (5) Distance from Fukushima Daini 183km to epicenter, 185 km to hypocenter (6) Data on tsunami a Inundation height (a) Seaside area (Ground height at base level of Onahama Port Construction site (hereinafter O.P.) + 4 m)
  • About +7 m*1 (flood depth about 3 m) *1) South side of Unit 1 seawater heat exchanger building. Highest point (b) Main building*2 area (Ground height O.P. + 12 m)*2 Reactor building and Turbine building
  • O.P. about +12~+14.5 m*2 (flood depth less than 2.5 m) *2) Between the area south of Unit 1 Main building and the important seismic isolation building.

Locally O.P. about+15~+16 m (flood depth about 3-4 m) b Flooded area The flooded area extended across the entire seaside area, but no entry of tsunami seawater into the main building area beyond the slope from the seaside area was observed. The tsunami run up was mostly from the southeast side of the main building area toward the road leading to the important seismic isolation building. As a result, flooding was limited only to the area surrounding the Unit 1 and 2 buildings and the south side of the Unit 3 building (no flooding around the Unit 4 building). (7) Arrival of the first wave of the tsunami March 11, 2011 3:22 pm Visual sighting) 16

3.4 Damage of Equipment 3.4.1 Damage by the earthquake The external power supply of Fukushima Daini consists of a total of four lines: 500 kV of Tomioka 1L and 2L and 66kV of Iwaido 1L and 2L, all from the Shin Fukushima substation. On the day of the earthquake, however, Iwaido 1L was out of service for inspection and only three lines were available. After the earthquake, Tomioka 2L went out of service at around 2:48 pm on March 11 due to damage to the breakers at the Shin Fukushima substation. After the earthquake, patrol inspection of facilities found damage at the arrester of Iwaido 2L, so after confirming that Tomioka 1L was continuously receiving all the power necessary for the station, Iwaido 2L was put out of service for restoration works in order to prevent the damage from spreading further.

As a result, after the earthquake, the external power supply was only available from a single line for the time being. However, Iwaido 2L resumed service at 1:38 pm on the next day, March 12, and Iwaido 1L was also revived at 5:15 am on March 13 after temporary restoration, giving the receiving configuration three lines. Maintaining the external power through this single transmission line made it possible to supply power to the available facilities, contributing a great deal to preventing the spread of the accident, and led to early convergence. All the equipment such as circuit breakers, etc.

at the substation and switching stations has basically the same specifications as at Fukushima Daiichi.

Fig 3.4.1-1 Fukushima Daini Outline Diagram of External Power Supply Ordinary High Voltage Power Panel (M/C) Ordinary High Voltage Power Panel (M/C) Emergency High Voltage Power Panel (M/C) Emergency High Voltage Power Panel (M/C) Emergency High Voltage Power Panel (M/C) Emergency High Voltage Power Panel (M/C) Out of service for check and maintenance Trip (Suspended) Circuit Breaker Dis-connector Transformer Main Power Generator Switching Station for Transformer Start-up Unit 1 Tomioka Line 1L Tomioka Line 2L Iwaido Line Line 1L Iwaido Line Line 2L 66 kV Startup Switching Station Switching Station for Auxiliary Boiler Unit 2 Unit 3 Unit 4 Fukushima Daini Nuclear Power Station Shin Fukushima Transformer Substation Suspension of Electric Cable (Out of Service) Tomioka Line 2L, Suspended (Suspended after the earthquake but before the tsunami) Iwaido Line Series 1, Suspended for repair works Under construction 18

3.4.2 Damage by the tsunami (1) Entry of flood water into Main building (Ref: Fig 3.4.2-1, 3.4.2-2) Inundation surrounding the main buildings of Fukushima Daini (reactor building and turbine building; Ground Level OP +12 m) was not significantly deep, with the exception of intensive run up on the south side of Unit 1. Intensive tsunami run up entered the Unit 1 building through the openings at ground level located on the south side of the reactor building (air intake louver for the emergency D/G, equipment hatch on the ground level) which flooded the reactor building (annex building) and caused the loss of function of all three units of emergency D/G, emergency power supply (for the C system and high pressure core spray system).

The depth of run up around Unit 2 through Unit 4 was not significant, and thus flooding into the reactor buildings or turbine buildings through the openings at ground level was not detected. However, flooding was confirmed in the basement of the reactor building of Unit 3 (Annex) and the basements of turbine buildings Unit 1 through Unit 3. It is thought that tsunami inundation entered the buildings through the cables and pipes leading to the underground trenches and ducts. Fig 3.4.2-1 Openings of flood entrance into the main building Fig 3.4.2-2 Flow path of flood to the main buildings of Fukushima Daini Openings on the ground where the flood entered the main building Openings leading to the underground trench duct where the flood entered the main building Unit 1 Unit 2 Unit 3 Unit 4 Seawater Heat Exchanger Building Turbine Building Reactor Building Unit 2-4, No significant water entry through the louver/hatch to the reactor building annex Unit 1, Water entry through louver/hatch to the reactor building annex Ground Level O.P.

12 m Ground Level O.P. + 4m Flood Height: O.P. + about 7 m Equipment Hatch Seawater Heat Exchanger Building Building Entrance Seawall Drainage Pump Power Panel Reactor Building Annex Main Reactor Building D/G Air Intake Louver Equipment Hatch Power Panel Reactor Building Annex Reactor Building Annex Main Reactor Building Reactor Building Annex 19

Table 3.4.2-1 Location of D/G and damages thereto Unit 1 Unit 2 Unit 3 Unit 4 Height of tsunami*1 About +9 m Ground Level O.P.+12 m Flood depth around main buildings [Inundation Height] Less than 2.5 m (nearly zero except around Unit 1) [O.P .about+12 m~+14.5 m] *2 A Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] B Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Building where D/G is installed [Floor] H Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Reactor Bldg. Annex [B2F] Reactor Bldg.

Annex [B2F] □:D/G unit flooded □:D/G unit not flooded *1 *2 Estimate at tide station. Actual measurement unknown because of instrument damage.

Locally about OP+15 – 16 m [flood depth about 3 – 4 m] in the area between the south side of the Unit 1 main building and the important quake proof building. (2) Damage situation Among the equipment for reactor cooling that was also damaged by the tsunami, the damage situation of the facilities that clearly show characteristics of equipment damage caused by the recent tsunami is explained as below.(Please refer to Table 3.4.2-2.) ① Emergency equipment cooling pump Units 1 through 4 use seawater to remove decay heat from the reactor. The emergency D/G unit also uses seawater to cool its engine.

Therefore, the pumps for the emergency equipment cooling water system (the seawater intake pump and the fresh water cooling pump sourced from seawater) are installed in the seaside area. These pumps are installed in the seawater heat exchanger building. The purpose of the overall layout in which seawater is not sent directly to the reactor building but to the intermediate seawater heat exchanger building, which is not a radiation control area, where a freshwater loop is installed with a heat exchanger and cooling pump for auxiliary equipment constituting an independent set of equipment cooling facilities, is to prevent seawater from mixing with reactor water and to improve maintenance works.

The pumps for the emergency equipment cooling water system are specified for outdoor use, but they were installed indoors in the heat exchanger building as part of the independent set of equipment cooling facilities. The ground level of the seaside area where the pumps for the emergency equipment cooling water system are installed had OP +4 m elevation, and its precautionary measures ensured safety against a tsunami height of 5.1 - 5.2 m, based on the tsunami height evaluation results in 2002 provided by the Japan Society of Civil Engineers “Tsunami Evaluation Technology”. However, this tsunami greatly exceeded expectations, and the motors of the pumps were submerged under the water and the system lost function.

The pumps for the emergency equipment cooling water system at Fukushima Daini were housed in the seawater heat exchanger buildings. The area surrounding the buildings was inundated to a depth of 3 m by the tsunami, and while there was no damage to the building structures, all the seawater heat exchanger buildings were flooded by seawater through the damaged doors and other openings on ground level. As a result, the 20

power panels and the motor of the pumps were submerged underwater and the total of eight emergency equipment cooling water systems lost function except for one system of Unit 3. In addition, the cooling system of the three D/G units, A, B and H installed for each reactor Unit also lost all function except for three systems: B and H of Unit 3 and H of Unit 4. ② Power panel The scale of the tsunami at Fukushima Daini was different from that at Fukushima Daiichi, and inundation of the main building was also different. Accordingly, the situations of power panel damage also differ as a result.

The Reactor building of Unit 1 (Annex), which was flooded by the tsunami, saw inundation on the emergency power panels of the C and H systems, but the D system power panel was not flooded and all the power panels of other reactor Units were free of damage.

Due to this situation, it was possible to distribute electric power received from outside sources to various pieces of equipment through these emergency circuits, making it possible to use the necessary facilities to cope with the emergency situation (distribution through Normal A and B2, Emergency C and D2, and high pressure core spray system H). On the other hand, the power panels in the seawater heat exchanger buildings located in the seaside area were all submerged in the tsunami because of flooding in the buildings, and seven power panels lost function, with the exception of one low voltage power panel (P/C) situated in the seawater heat exchanger building of Unit 3.

Therefore, the residual heat removal seawater system lost function except for one system of Unit 3 out of the total of eight.

Table 3.4.2-2 Damage situation of the cooling pumps for emergency equipment and emergency P/C located in the seawater heat exchanger buildings after the tsunami Seawater Pump (RHRC, RHRS and LLCW) ○ Usable △ Out of service due to flooding of Power Panel × Out of service due to flooding of Power Panel and Motor Unit 1 Unit 2 Unit 3 Unit 4 Emergency P/C Unit 1 Unit 2 Unit 3 Unit 4 ○ Usable × Out of service due to flooding North side South side North side South side North side South side North side South side North side South side North side South side North side South side North side South side 2nd Floor Ground Floor Location of Installati on Location of Installati on Grou nd Floor 21

Emergency Diesel Generator In the Fukushima Daini power station, each reactor Unit has three (A, B, H) emergency diesel generators (hereinafter referred to as "emergency D/G"). Unit 1 lost all three emergency D/Gs because the tsunami had entered the reactor building (Annex) through the opening at the ground level. Some of the emergency D/Gs which were able to avoid the flooding still lost function because of the loss of diesel engine cooling due to the flooding of the power panel and the pump motor for the cooling system. The cooling system of the emergency D/G was lost for most of the systems except for three: B and H of Unit 3 and H of Unit 4.

As a result, nine D/Gs lost function: A, B and H of Unit 1, A, B and H of Unit 2, A of Unit 3 as well as A and B of Unit 4.

However, Fukushima Daini had a continuous supply of electric power from the external sources and there was no need to activate such surviving emergency D/G after all. ④ Situation of other outdoor damage In the Fukushima Daini power station area, no major equipment and/or structure was observed being washed up by the tsunami to the main building area (elevation OP +12 m). However, five cases of openings/holes caused by the tsunami washing away or damaging the lid of the hatch duct in the main building area have been reported. Source; Tokyo Electric Power Company The impact of Tohoku-Chihou Taiheiyo-Oki Earthquake to Nuclear Reactor Facilities at Fukushima Daini Nuclear Power Station (May 9, 2012) Fukushima Nuclear Accident Analysis Report (June 20, 2012) Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company Final Report (July 23, 2012) 22

4. Response to the accident at Fukushima Daini The status of the accident at Fukushima Daini has already been reported in detail in the reports of TEPCO and the Investigation Committee of the Government. Therefore, this report puts the emphasis on describing the situation, including points of suggestion in considering the lessons learned, and giving a brief overview of the other points. Fig 4-1 shows the operational status of the responses of Units 1 through 4, and Figs 4-2 to 4-5 show the operational status of each Unit in conjunction with the changes in the main parameters of each Unit.

8:00 12:00 0:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 March 14 March 15 March 16 12:00 0:00 4:00 8:00 12:00 16:00 20:00 16:00 20:00 March 12 March 13 20:00 0:00 4:00 8:00 4:00 16:00 Unit 4 Unit 1 Unit 2 12:00 8:00 12:00 March 11 Unit 3 16:00 20:00 0:00 Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 1:24 on March 14) ▲17:53 D/W cooling system manual start ▲0:00 MUWC alternative water injection start ▲D/W spray (7:10 – as appropriate) S/C cooling by FCS cooling water (MUWC)(6:20~7:20) ▲S/C spray (7:37 – as appropriate) ▽9:40 MUWC alternative water injection Stopped Configuration of pressure proof vent-line (10:21 – 18:30) ▲20:17 RHRS(B) Manual start ▲21:03 RHRC(D) Manual start ▲1:24 RHR(B) Start  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency ▲1:44 Emergency component cooling system (B) manual start ▲3:39 S/C spray by RHR (B) start ▲10:05 Reactor water injection by means of RHR (B) LPCI mode ▲16:30 SFP water injection by FPMUW start ▲17:00 Reactor cold shutdown ▲20:26 FPC (B) circulation operation start ▲0:42RHR(B) SFP cooling start ▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip ▽15:33 CWP(C) Manual stop Water injection by RCIC (15:36 – 4:58) ▲15:36 MSIV manual full-close ▽15:57 CWP(A,B) Automatic stop ▲Rapid depressurization (3:50 – 4:56)] ▲▽15:34 Emergency D/G H automatic start followed by immediate trip Water injection by RCIC (15:41 – 4:53) ▲15:34 MSIV manual full-close ▲15:35 RHR(B) Manual start ▽15:38 RHR(B) Stop ▽15:35 CWP(C) Manual stop, (A and B) automatic stop ▲▽15:41 Emergency D/G A and B automatic start followed by immediate trip Report pursuant to Article 10 of the Act on Special Measures Concerning special Law Nuclear Emergency Preparedness (loss of reactor heat removal function) (18:33 on March 11 – 7:13 on March 14) Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:32 on March 12 – 15:52 on March 14) ▲20:02 D/W cooling system manual start ▲4:50 MUWC alternative water injection start ▲D/W spray (7:11 – as appropriate) S/C cooling by FCS cooling water (MUWP) (6:20 – 7:52) ▲S/C spray (7:35 – as appropriate) Configuration of pressure proof vent-line (10:33 – 10:58) ▲15:50~as appropriate Reactor depressurization ▽10:12 MUWC alternative water injection stopped ▲3:20 Emergency component cooling system (B) manual start ▲3:51 RHRS(B) Manual start ▲5:52 RHRC(B) Manual start ▲7:13 RHR(B) Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Nuclear Emergency ▲7:50 RHR(B)S/C Spray start ▲10:48 Reactor water injection by means of RHR (B) LPCI mode ▲18:00 Reactor cold shutdown ▲1:28 RHR(B) SFP cooling start ▽15:34 CWP(C) Manual stop ▲▽15:35 Emergency D/G A, B and H automatic start followed by immediate trip of A ▲15:36 RHR(B) S/C cooling start ▲15:37 MSIV manual full-close ▽15:38 CWP(B) Manual stop Water injection by RCIC (16:06 – 23:58) ▽16:48 CWP(A) Manual stop ▲19:46 RHR(B) S/C cooling  Switch to LPCI mode ▲20:07 RHR(B) LPCI mode  Switch to S/C cooling ▲20:12 D/W cooling system manual start ▲22:53 MUWC alternative water injection start (unknown when stopped) Configuration of pressure proof vent-line (12:08 – 12:13) ▲0:06 RHR(B) Commencement of configuration of SHC mode system ▽1:23 RHR(B) Manual stop, prepare for SHC mode being on ▲2:39 RHR(B) Manual start (S/C cooling start) ▲2:41 RHR(B)S/C Spray start ▽7:59 RHR(B) Manual stop ▲9:37 RHR(B) Manual start (commencement of SHC) ▲12:15 Reactor cold shutdown ▲17:42 FPC Hx cooling water switch-over (RCW  RHRC) ▲10:30 SFP water temperature approximately 38°C (before earthquake) ▲ 10:30 SFP water temperature approximately 32.5°C (before earthquake) ▲ 22:30 SFP water temperature approximately 32.5°C (before earthquake) ▽15:33 CWP(C) Manual stop ▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip of A and B ▽15:34 CWP(A,B) Automatic stop ▲15:36 MSIV manual full-close ▲15:36 RHR(A,B) Manual start ▽15:38 RHR(A) Manual stop ▽15:41 RHR(B) Automatic stop Water injection by RCIC (15:54 – 0:16) Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 15:42 on March 14) ▲19:14 D/W cooling system manual start ▲0:16 MUWC alternative water injection start ▲7:35 Alternative containment vessel spray start ▽17:25 MUWC alternative water injection stopped Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergencys (loss of pressure suppression function) (6:07 on March 12 – 7:15 on March 15) S/C cooling by FCS cooling water (MUWP)(7:23 – 22:14) ▲11:17 HPCS pump start (S/C agitation operation) Configuration of pressure proof vent-line (11:44 – 11:52) ▲12:32 Reactor water injection switch-over (MUWC  HPCS) ▽13:48 Water injection by HPCS stop ▲11:00 Emergency component cooling system (B) manual start ▲13:07 RHRS(D) Manual start ▲14:56 RHRC(B) Manual start ▲15:42 Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures ConcerningSpecial Law for Nuclear Emergency ▲16:02 RHR(B)S/C Spray start ▲18:58 Reactor water injection by means of RHR (B) LPCI mode start ▲7:15 Reactor cold shutdown ▲16:35 FPC Hx cooling water switch-over (RCW → RHRC) ▲ 20:59 RHR(B) SFP cooling start (7:30 on March 18: SFP water temperature approximately 35°C (before earthquake)) ▲Around 22:00 Commence site observation (around Hx / B) ▲Around 6:00 Equipment and materials arrived ▲Around 23:30 Completion of temporary cable-laying ▲Before dawn: Cable-laying, Unit 1 being of priority (Unit 2  Unit 1) Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:22 on March 12 – 10:15 on March 14) Chart 4-1: Situation of action in response to the Unit 1 – Unit 4 accident 24

Unit 1 8:00 12:00 0:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 March 14 March 15 March 16 12:00 0:00 4:00 8:00 12:00 16:00 20:00 March 11 16:00 20:00 March 12 March 13 20:00 0:00 4:00 8:00 4:00 8:00 12:00 16:00 12:00 16:00 20:00 0:00 Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of reactor heat removal function) (18:33 on March 11 – 1:24 on March 14) ▲0:00 MUWC alternative water injection start ▲D/W spray (7:10 – as appropriate) S/C cooling by FCS cooling water (MUWC) (6:20 – 7:20) ▲S/C spray (7:37 – as appropriate) ▽9:40 MUWC alternative water injection stopped Configuration of pressure proof vent-line (10:21 – 18:30) ▲20:17 RHRS(B) Manual start ▲21:03 RHRC(D) Manual start ▲1:24 RHR(B) Start  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency ▲1:44 Emergency component cooling system (B) manual start ▲3:39 S/C spray by RHR (B) start ▲10:05 Reactor water injection by means of LPCI mode ▲16:30 SFP water injection by FPMUW start ▲17:00 Reactor cold shutdown ▲20:26 FPC(B) Circulation operation start ▲0:42 RHR(B) SFP cooling start ▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip ▽15:33 CWP(C) Manual stop Water injection by RCIC (15:36 – 4:58) ▲15:36 MSIV manual full-close ▽15:57 CWP(A,B) Automatic stop ▲Rapid depressurization (3:50 – 4:56) ▲15:50 – as appropriate Reactor depressurization ▲10:30 SFP water temperature approximately 38°C (before earthquake) 1000 2000 3000 4000 5000 6000 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Reactor water level [mm] (fuel area conversion) Reactor pressure [MPa] 50 100 150 200 250 300 350 400 450 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 20 40 60 80 100 120 140 160 D/W pressure [kPa abs] S/C pressure [kPa abs] S/C water temperature [°C] [mm] [MPa] [kPa] Measurement missing due to paper jam [°C] ▲17:53 D/W cooling system manual start Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:22 on March 12 – 10:15 on March 14) Chart 4-2: Situation of action in response to accident and plant parameter of Unit 1 25

  • Unit 2 8:00 12:00 0:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 March 14 March 15 March 16 12:00 0:00 4:00 8:00 12:00 16:00 20:00 March 11 16:00 20:00 March 12 March 13 20:00 0:00 4:00 8:00 4:00 8:00 12:00 16:00 12:00 16:00 20:00 0:00 1000 2000 3000 4000 5000 6000 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Reactor water level [mm] (fuel area conversion) Reactor pressure [MPa] [mm] [MPa] ▲▽15:34 Emergency D/G H automatic start followed by immediate trip Water injection by RCIC (15:41 – 4:53) ▲15:34 MSIV manual full-close ▲15:35 RHR(B) Manual start ▽15:38 RHR(B) Stop ▽15:35 CWP(C) Manual stop, (A and B) Automatic stop ▲▽15:41 Emergency D/G A,B Automatic start followed by immediate trip Report pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergencys (loss of reactor heat removal function) (18:33 on March 11 – 7:13 on March 14) Report pursuant to Article 15 of the Act on Special Measures Concerning Special Law for Nuclear Emergency (loss of pressure suppression function) (5:32 on March 12 – 15:52 on March 14) ▲20:02 D/W cooling system manual start ▲4:50 MUWC alternative water injection start ▲D/W spray (7:11 – as appropriate) S/C cooling by FCS cooling water (MUWP) (6:20 – 7:52) ▲S/C spray (7:35 – as appropriate) Configuration of pressure proof vent-line (10:21 – 18:30) ▽10:12 MUWC alternative water injection stopped ▲3:20 Emergency component cooling system (B) manual start ▲3:51 RHRS(B) Manual start ▲5:52 RHRC(B) Manual start ▲7:13 Start (S/C cooling mode)  Call-off pursuant to Article 10 of the Act on Special Measures Concerning Special Law for Nuclear Emergency ▲7:50 RHR(B) S/C spray start ▲10:48 RHR(B) Reactor water injection by means of LPCI mode ▲18:00 Reactor cold shutdown ▲1:28 RHR(B) SFP cooling start ▲15:41 – as appropriate Reactor depressurization as
  • :D/W圧力 [kPa abs]
  • :S/C圧力 [kPa abs] 50 100 150 200 250 300 350 400 450 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 20 40 60 80 100 120 140 160 D/W pressure [kPa abs] S/C pressure [kPa abs] S/C water temperature [°C] [°C] [kPa] ▲ 10:30 SFP water temperature approximately 32.5°C (before earthquake) Chart 4-3: Situation of action in response to accident and plant parameter of Unit 2 26

Unit 3 8:00 12:00 0:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 March 14 March 15 March 16 12:00 0:00 4:00 8:00 12:00 16:00 20:00 March 11 16:00 20:00 March 12 March 13 20:00 0:00 4:00 8:00 4:00 8:00 12:00 16:00 12:00 16:00 20:00 0:00 1000 2000 3000 4000 5000 6000 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Reactor water level [mm] (fuel area conversion) Reactor pressure [MPa] ▽15:34 CWP(C) Manual stop ▲▽15:35 Emergency D/G A, B and H automatic start followed by immediate trip of A ▲15:36 RHR(B) S/C cooling start ▲15:37 MSIV manual full-close ▽15:38 CWP(B) Manual stop Water injection by RCIC (16:06 – 23:58) ▽16:48 CWP(A) Manual stop ▲19:46 RHR(B) S/C cooling  switch-over to LPCI mode ▲20:07 RHR(B) LPCI mode  switch-over to S/C cooling ▲20:12 D/W cooling system manual start ▲22:53 MUWC alternative water injection start (unknown when stopped) Configuration of pressure proof vent-line (12:08 – 12:13) ▲0:06 RHR(B) Configuration of SHC mode system start ▽1:23 RHR(B) Manual stop (prepare for SHC mode being on) ▲2:39 RHR(B) Manual start (S/C cooling start) ▲2:41 RHR(B) S/C spray start ▽7:59 RHR(B) Manual stop ▲9:37 RHR(B) Manual start (SHC start) ▲12:15 Reactor cold shutdown ▲17:42 FPC Hx cooling water switch-over (RCW  RHRC) ▲ 22:30 SFP water temperature approximately 32.5°C (before earthquake) ▽15:33 CWP(C) Manual stop ▲▽15:34 Emergency D/G A, B and H automatic start followed by immediate trip of A and B ▲11:00 Emergency component cooling system (B) manual start Measurement missing due to paper jam 50 100 150 200 250 300 350 400 450 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 20 40 60 80 100 120 140 160 D/W pressure [kPa abs] S/C pressure [kPa abs] S/C water temperature [°C] [mm] [kPa] [MPa] [°C] Chart 4-4: Situation of action in response to accident and plant parameter of Unit 3 27

You can also read